This application claims the priority of German Application No. 198 33 613.6, filed Jul. 25, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an optical data bus for a vehicle with transmit/receiving units that exchange data messages over optical connecting lines and which are supplied with electrical energy.
Such data buses are becoming increasingly important in vehicles. Even when the vehicle is parked, the TRUs must be at least partially ready to receive. For this purpose, at least the optical receiver, a phototransistor for example, must be supplied with operating voltage. A current of several mA then flows. Added together, these currents, admittedly small individually, produce a high power draw through a large number of receivers when the vehicle is parked.
The goal of the invention is to provide a data bus of the type recited at the outset that has a low power draw when the vehicle is parked, but in which operating readiness is simultaneously guaranteed.
The invention achieves this goal by providing an optical data bus for a vehicle with transmit/receive units (TRUs) that exchange data messages over optical connecting lines and which are supplied with electrical energy. The invention is characterized in that the receiving TRU can be deactivated to reduce energy consumption and then reactivated for a short time. Further, the transmitting TRU emits a light pulse whose length is greater than the length of its resting phase.
The activation of the receiving units, each only for a short time, produces a definite reduction in the energy requirement. This requirement is only a fraction of that during continuous operation. The fraction is determined by the cycle ratio, in other words the ratio of the ON times to the OFF times. For example, if the cycle ratio is 1:1000, the power requirement is reduced practically to a thousandth, since the current draw of the electronic parts that produce the cyclic operation of the receiver is negligible in this technology.
The operational readiness of the data bus is ensured at all times. The individual TRUs are activated over the optical connecting lines. Additional or alternative activation by the electrical power supply is not necessary.
Advantageous embodiments of the invention are described herein. One of the problems which the invention overcomes concerns the time interval or frequency with which the individual TRUs are activated. One possibility is to activate the TRUs briefly at regular intervals. The advantage of this is that the transmitting TRUs each must emit only light pulses of a constant length.
On the other hand, a further reduction of the power consumption can be achieved when the resting phases are kept as long as possible. For example, they can depend on how long the vehicle has already been parked and can be lengthened in direct ratio to this time. This however creates the necessity for varying the length of the light pulses.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.